Stereoselective effect of tranylcypromine enantiomers on brain serotonin

Brain levels of 5-HT, 5-HIAA and L-tryptophan were measured in reserpinized rats given the enantiomers of tranylcypromine (TCP). (+)-TCP (1.5-30 mg/kg) increased levels of 5-HT, whereas (-)-TCP failed to affect 5-HT levels. (+)-TCP at high dosage (30 mg/kg) decreased brain levels of 5-HIAA, whereas (-)-TCP failed to affect 5-HIAA levels. Neither (+)-TCP nor (-)-TCP influenced brain levels of L-tryptophan. The effects of (+)-TCP on behavior resembled those of drugs which influence 5-HT processes, whereas (-)-TCP failed to produce 5-HT-dependent behaviors. The findings support the notion that TCP enantiomers have stereoselective effects on serotonergic mechanisms.